How to model a jagged cave?
Since the question was on particles here's my take on it.

Start with a cylinder.



Subdivide it a number of times but make it somehow irregular with a fractal:



Then create some cuboid object (I put it on a different layer so that is out of the way...)



Then on the cylinder create a particle system.

Make the start and end frame 1 (so that all of particles are present on frame 1)

Use the cuboid object as the render object.

For rotation select the axis that makes sense depending on how your object is placed (in this case, the object X axis works for me), and set the random rotation to Zero.

Then give the render object some variation on size.

Optionally you can disable the emitter so that only the cuboids show on the render and not the original cylinder.







Giving the particles a bit of randomness might make them more interesting.